The invention relates to a clamp, particularly a battery terminal clamp for connecting an electric cable to a terminal of a car battery, having two clamping jaws extending generally linearly from a closed region to an open region having two free ends which are positioned opposite each other, a clamping receiver disposed between the closed end and the open end, the clamping jaws separated by a clamping gap, a tensioning device which produces a tensioning force acting perpendicular to the horizontal plane, and sloping surfaces and corresponding counter-surfaces extending away from the clamping receiver along the free ends and/or tensioning device. The sloping surfaces and counter-surfaces interact in a sliding manner to convert the tensioning force into a clamping force, moving the clamping jaws toward each other. The angle between the sloping surfaces and the horizontal plane is greater at a point near the closed end than at a point further away from the closed end.
In a car battery terminal clamp of the type shown in German Patent Specifications DE 3,811,629 C1 and DE 4,138,547 C1, the tensioning device contains a tensioning screw which is arranged parallel to the receiving direction of the battery terminal and onto which a threaded nut is screwed, which makes it possible for the tensioning device to be operated conveniently from the top of the car battery. The conversion of the tensioning force into a clamping force, running transversely to the clamping jaws is effected by means of sloping surfaces and counter-surfaces which are provided on a separate clamping piece and/or on the free ends of the clamping jaws and interact with one another in a sliding manner, the free ends of the clamping jaws being pressed towards one another when the tensioning screw is tightened. These known sloping surfaces and counter-surfaces consist in each case of flat surface sections which extend approximately radially away from the clamping receiver, i.e. perpendicular to the receiving direction of the terminal and to the direction of movement of the free ends of the clamping jaws, and are inclined perpendicular to said direction uniformly by a specific, given slope angle.
The design of the clamp with two clamping jaws which are tensioned on one side, i.e. those whose ends are fixed relative to each other in one end region while their opposite ends are movable relative to each other to produce the clamping effect, results in the clamping movement not consisting of a pure translatory movement of the clamping jaws relative to each other, but primarily of a rotary movement of the clamping jaws about a local center of rotation which generally changes its position in the course of the clamping movement. As a consequence of this rotary movement, outer regions, i.e. regions located further away from the clamping receiver, travel over a greater path during the clamping movement than regions located further inward, i.e. regions near the clamping receiver. This, in turn, means for the above-mentioned, known terminal clamps with the sloping surfaces and counter-surfaces designed in each case as flat surfaces that said surfaces only interact in a planar manner in a single position in which the sloping surfaces extend precisely parallel to one another. The more the actual position of the clamping jaws deviates in each case from this single position, the more the planar pressing contact of the sloping surface and counter-surface is lost, in particular towards the outer end edge of the jaw while the contact pressure towards the inner region near the clamping receiver increases. This results in a transition from a planar contact pressure to a linear and finally point-contact pressure, which entails a correspondingly high material stress when generating the clamping effect. The displacement of the force acting in the direction towards the local center of rotation additionally has the effect of increasing the force due to the laws of leverage and thus of stressing the material. The high point-type force loading means a restriction in the use of comparatively soft materials, such as lead-coated brass.
Reference is made in German Patent Specification DE 4,226,563 C1 to the problem of a contact surface between the sloping surfaces and the counter-surfaces being reduced during the clamping movement by tightening the tensioning device. To maintain an improved contact between the sloping surfaces and the counter-surfaces and thus a greater area to absorb the clamping force, a terminal clamp of the generic type for a battery or accumulator pole is proposed in that publication, in which the sloping surfaces on the clamping jaws are curved in such a way that their height lines lying in planes parallel to the plane of the clamping movement extend along arcs of the same curvature, the counter-surfaces provided on a clamping piece being formed to be curved in a complementary manner. The sloping surfaces therefore form parts of the outer surface of a cutting cylinder and have, at each point on their course curved parallel to the clamping plane, a constant angle between the surface horizontal and the direction perpendicular to the clamping plane and thus a slope angle of equal size at each point.
The object of the present invention is to provide a battery terminal clamp which can be produced with relatively little outlay and in which the interacting sloping sliding surfaces maintain maximum contact so that the contact pressure remains as low as possible in any clamping position.
This object has been achieved according to the present invention by providing at least one sloping surface designed such that its slope is greater at the level of an inner cutting plane near the clamping receiver than at the level of an opposite, outer cutting plane farther away from the clamping receiver. This solution takes account, in a fitting manner, of the fact that the outer regions of the free ends of the clamping jaws undergo a greater change in distance during the clamping operation than their inner regions, in such a way that, during the entire clamping operation, i.e. in any clamping position, the sloping surface and the counter-surface remain in contact at the level of the outer plane. This already provides an improvement compared to the above-mentioned known arrangement based on aspects of the laws of leverage since, according to the invention, in the worst case an only point-type contact of the sloping surface and counter-surface can result at the level of the outer plane, which already results in a lesser point-type contact pressure than in the case of a point-type contact at the level of the inner plane. Additionally, however, due to the selection of the greater slope angle according to the invention for the inner region of the surface of section, the contact between the sloping surfaces and counter-surfaces normally remains intact in all clamping positions even in that region. The resulting two-point contact has the effect of further reducing the force loading. Depending on the further individual design of the sloping surface and counter-surface interacting therewith, the contact pressure can be reduced further where a linear or planar contact of the sloping surface and counter-surface resting against one another over their entire surface, or at least along the inner and outer regions, remains intact in any clamping position. In this case, a complex shaping of curved surface sections is not absolutely essential.
In one preferred embodiment of the present invention, continuations and slot openings are located at a different level in relation to the clamping receiver and interact tangentially to the clamping receiver with respective boundary sides. The boundary sides are preferably formed as flat surface sections, the two inner, interacting sections both being designed to be inclined by the greater slope angle and the two outer sections both being designed to be inclined by the smaller slope angle. This design allows, for example, an integral design of the clamp, apart from the tensioning screws and associated threaded nuts, by suitable modification of appropriate, known clamps mentioned above.
In an alternative design of the present invention, a separate, U-shaped clamping piece is provided wherein the free ends of the clamping jaws can be squeezed together, the inner sides of the limbs providing the sloping surfaces with which counter-surfaces formed at the ends of the clamping jaws interact in a sliding manner. In a further development of this design, the sloping surfaces on the inner sides of the limbs are composed of two flat triangular surfaces which are tilted towards each other. This design of the sloping surfaces, on the one hand, can be implemented without great technical complexity and, on the other hand, constitutes a good compromise with respect to an ideal design of the sloping surfaces whose course corresponds to a square surface which is twisted in the longitudinal direction of the clamping component.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.